The present invention relates to lighting instruments, and especially to devices and apparatus for controlling the distribution of light energy in non-imaging illumination applications.
In stage lighting, it is often desirable to expand the light beam from a so-called wash luminaire to illuminate a broader area. A wash luminaire can produce such an effect using a light source and a concave reflector which are moveable with respect to a lens, such as disclosed in U.S. Pat. No. 3,428,800; or in U.S. Pat. No. 3,665,179. The divergence angle of the light beam varies depending upon the position of the source and reflector with respect to the lens. Popular variable-divergence luminaires such as the Cadenza PC manufactured by Rank Strand of the United Kingdom and the 2KW Fresnel manufactured by Mole-Richardson of California and others, use such an optical system to control the divergence angle of the light beam projected by the luminaire. A positive, or convex, front lens illuminated by a lamp and retroreflector combination produces a substantially columnar light beam and projects a relatively small pool of light when the lamp is placed at the focus of the lens. As the lamp and reflector combination is moved in either direction away from the focus of the lens, the beam diverges from columnar to project a larger pool of light. Such a system is quite large and requires many inches of travel for the lamp and reflector combination along the optical axis of the lens. The carrier mechanism of these luminaires is typically manually adjustable and the large glass front lens, typically eight to ten inches in diameter, is thick and heavy even with the significant weight reduction gained by the Fresnel design used by Mole-Richardson.
Another common system for controlling the divergence angle of a light beam is disclosed in U.S. Pat. No. 4,602,321; and uses a lamp, which is movable with respect to a parabolic reflector. When the lamp is placed at the focus of the reflector, a substantially columnar light beam emerges and projects a small pool of light. As the lamp is moved rearwardly along the optical axis of the reflector and away from the focus of the reflector, the beam diverges from columnar to form a larger pool of light. This system requires an adjustable carriage for the lamp socket and frequently requires provisions for minor (manual) adjustments along two additional axes orthogonal to the optical axis, so as to maintain proper alignment of the lamp on the optical axis, in addition to motorized adjustment along the optical axis for controlling beam divergence.
Many commonly used systems for controlling the divergence angle of a light beam use two or more lens elements is series and in combination with a fixedly mounted lamp and a fixedly mounted reflector. In these systems, one or more of the lens elements are movable with respect to the lamp and reflector to vary the divergence angle of a light beam formed thereby. Some common examples are disclosed in U.S. Pat. Nos. 2,076,240; 2,650,292; 2,950,382; 3,302,016; 3,594,556; 4,462,067; 4,519,020; 4,709,311; 4,739,456; 5,029,992; 5,404,283; among others. Some of these systems are used in image-projecting applications in which a hard-edged spot of light is projected onto a distant surface such as a stage floor or backdrop, and may also be used to project complex images formed by objects placed in a focal plane of the projection lens system, such as described, for example, in U.S. Pat. No. 4,779,176.
Another, unique system for controlling the energy distribution of a light beam in a non-imaging application is disclosed in U.S. Pat. No. 5,774,273; and uses a variable-geometry liquid-filled lens having a deformable, transparent membrane supported by a transparent, multi-cellular structure forming an array of variable-power lenslets. An optically clear liquid is pumped into or out of the structure to deform the membrane into an array of convex or concave lenslets having adjustable optical power to control energy distribution. A motorized pump is used as the actuator, and the system may be operated by remote control.
A solid-state zoomable beamspreader is disclosed in U.S. Pat. No. 6,282,027, which is incorporated herein by reference. The beamspreader comprises first and second multiple-lens arrays including a plurality of plano-convex lenses in correspondence with a plurality of plano-concave lenses having matched, curved optical surfaces. In a zero-power state, the two multiple-lens arrays are very closely spacedxe2x80x94possibly touching at one or more placesxe2x80x94so that the matched convex and concave surfaces effectively cancel each other optically. But, as the two arrays are separated coaxially along the axis of a light beam, beam divergence angle increases as a function of the distance of separation. A large amount of beam divergence is obtained when the curved surfaces of the plano-concave lenses of the second array are positioned beyond the focal points of the plano-convex lenses of the first array.
The plano-convex lenses and the corresponding plano-concave lenses disclosed in U.S. Pat. No. 6,282,027 are characterized as having substantially equal but opposite optical power so that the combined optical power of the first and second multiple lens arrays is zero when the two lens arrays are separated by zero distance. Practical mechanical considerations in the design of a motor-driven apparatus for an automated lighting instrument make it desirable to prevent two glass surfaces from actually touching each other. Therefore a design methodology is required which does not require zero separation of the lens elements to achieve a zero-power state.
In accordance with the present invention, a first multiple-lens array comprises positive-power lenses and produces multiple bundles of converging light rays. A second multiple-lens array comprises negative-power lenses and produces multiple bundles of collimated light rays when the two multiple-lens arrays are axially separated. As axial separation of the two multiple-lens arrays increases, divergence of the entire beam of light increases.